1. Field of the Invention
The invention relates to electrical apparatus and, more particularly, to an emergency system for disconnecting a multibranch electrical power distribution circuit from a source of electrical power.
2. Description of the Prior Art
Emergency electrical power interrupting "panic buttons" are widely used in laboratories, shops, factories, and commercial establishments. Such systems normally consist of large, easily seen red pushbutton switches located in readily accessible places to provide for rapid interruption of electrical power should an emergency occur. In prior art systems, the panic button operates a momentary contact switch which is used to energize the trip coil of a circuit breaker protecting the power distribution circuit. Thus, separate wiring must be provided between the circuit breaker and each location wherein it is desired to place a panic button. The cost and complexity of this additional wiring has often meant that the number of panic buttons installed has been less than would be desirable. In other situations, this cost and complexity has completely ruled out the installation of such an emergency power interruption system.
In most industrial and commercial installations, and in many residential installations, the National Electric Code calls for the inclusion of ground fault protective capability in addition to overload current protection. Such ground fault protective equipment is normally designed to deenergize the associated electrical power distribution network upon detection of ground fault current levels much less than the overload trip levels. For example, many residential ground fault circuit breakers are designed to trip upon detection of 5 milliamperes of ground fault current. In addition, many ground fault circuit breakers include means for tripping the circuit breaker upon detection of a grounded neutral conductor.
It is desirable to provide an emergency power interruption system which does not require wiring other than the power conductors themselves and which uses the sensitive ground fault detection capability and grounded neutral conductor detection capability of ground fault circuit interrupters already existing in many installations. It is also desirable to provide an emergency power interruption system which is operable upon a multibranch power distribution network regardless of whether the branch circuit breakers are open or closed.